The invention relates to a Time Division Multiple Access (TDMA) synchronization system. The invention is particularly concerned with communications satellite relay systems.
In TDMA systems currently envisaged for commercial communication satellites, the earth stations would transmit their respective digital data traffic at specified respectively corresponding times within an overall time frame. In such proposals, a special carrier frequency burst transmitted from a reference station defines the start of the time frame and must be received by all other earth stations. Comparison of the measured time difference between the received reference burst and a particular station's own received traffic data burst is used as a basis for the control of that station's transmitted traffic data burst timing. In such systems, special transmissions, which do not interfere with the TDMA traffic data transmissions of the other earth stations must also be made by any earth station desiring to initiate its entry into the operating TDMA system. However, provisions may also be made for rapid re-entry after short interruptions without going such an the initial acquisition procedure.
Such a prior art system requires each ground station to be able to receive its own TDMA traffic data transmission. In satellites. which have spot beam antennas for the majority of the traffic, this prior art the above synchronization scheme may not be possible or desirable.
In future satellite relay systems there may be situations where the constraints imposed by the system demand an alternative synchronization system such as the invention described below.